1) Field of the Invention
The present invention relates to radio frequency identification (RFID) tags and a method of manufacturing of the RFID tags.
2) Description of the Related Art
Recently, there is provided an RFID tag such as a non-contact IC card that receives a power supply and information from an external device such as a reader/writer without contact and transmits information to the external device using a radio wave. This RFID tag includes an antenna pattern provided on a plastic or paper base material, and an IC chip. The antenna pattern and a capacity element incorporated in the IC chip form a resonant circuit. The RFID can communicate with the external device by radio through the antenna pattern.
As a method of manufacturing the RFID tag, what is called a flip-chip mounting technique as shown in FIG. 9 is publicly known. An RFID tag as shown in FIG. 10 is manufactured according to this mounting technique. FIG. 9 is an explanatory diagram of a conventional method of manufacturing an RFID tag, and FIG. 10 is a cross-sectional diagram of a conventional RFID tag.
A “tape mounting and dicing step” is first explained. As shown in FIG. 9, a semiconductor wafer 4 undergone a grinding step is fixed with a dicing tape 8 on a table 2. This semiconductor wafer 4 is cut into IC chips with a known dicing device 6, and each IC chip 10 is cut out.
At a “dice picking step” as shown in FIG. 9, each IC chip 10 is extracted from the dicing tape 8 with a pin 9a and an arm 9b of a dice picking device, and is moved to a predetermined position. At a “bump forming step”, bumps 11 as connection metal protrusions are formed on a chip electrode 10a of each IC chip 10. Each bump 11 can be formed on a substrate 100 instead of on the chip electrode 10a. 
On the other hand, at an “antenna pattern forming step”, an antenna pattern 16 is screen printed on the substrate 100. In other words, print masks 12 are disposed at predetermined positions on the substrate 100. A known conductive paste 13 is coated (printed) onto the substrate 100 by moving a squeegee 14, thereby printing the antenna pattern 16 at a necessary position on the substrate 100.
At an “under-fill (UF) coating step”, an under-fill 18 to fix and protect the bumps 11 and the IC chip 10 is coated at positions of the substrate 100 where the IC chips 10 are mounted. At a next “IC chip mounting step”, the bumps 11 are connected to the antenna pattern 16, and the IC chip 10 is mounted on the substrate 100 such that the chip electrode 10a becomes conductive to the antenna pattern 16.
After the IC chip 10 is mounted on the substrate 100, the substrate 100 is covered with a cover sheet 120 at the next “laminating step”. By covering with the cover sheet 120, an aggregate 130 of RFID tags is formed. Simultaneously, each IC chip 10 and each antenna pattern 16 of the aggregate 130 are protected from an external environment such as external force and moisture. At a “slitting step”, individual RFID tags 130a are cut out from the aggregate 130 of the RFID tags with a cutter.
Japanese Patent Application Laid-Open No. 2003-242472 discloses a method of manufacturing an RFID tag. This method includes: a step of forming recess corresponding an external shape and a depth of an IC chip at intervals on a running web material; a step of leaving each one IC chip having the external shape and a shape corresponding the depth into the recess of the web material in an engaged state; a step of printing an antenna pattern or a print circuit according to an inkjet method so as to be connected to a chip electrode of the IC chip engaged in the recess; and a step of covering the entire surface including the recess of the web material engaged with the IC chip and printed with the antenna pattern, with a film.
A recess 102 as shown in FIG. 11 is disclosed as the recess of the RFID tag manufactured according to the above method. In other words, the recess 102 to be engaged with the IC chip 10 is formed on the substrate 100 according to an embossing, for example. In this case, a portion where the recess 102 is formed on the substrate 100 is protruded from a back surface of the substrate 100 by a predetermined distance t. FIG. 11 is a cross-sectional diagram of the conventional recess formed by embossing.
According to the above first conventional method of manufacturing an RFID tag, however, the bump 11 needs to be provided on the chip electrode 10a or on the substrate 100. Further, the IC chip 10 must be fixed with the under-fill 18, which is troublesome and costly.
According to the above second conventional method of manufacturing an RFID tag, the external surface of the recess 102 of the manufactured RFID tag protrudes from the back surface of the substrate 100. Since the back surface of the RFID tag is not flat, stress is easily concentrated on the protruded portion when the RFID tag is stuck to a product or the like and used, possibly breaking the RFID tag.
When the RFID tag is stuck to a flat surface of a product or the like with an adhesive or the like, the protruded portion hinders the adhesion, and generates a space between the tag and the stuck surface. Therefore, the RFID tag is easily peeled off from the product.